This invention refers to a socket for light-bulbs, comprising first and second contact members for electric contact between two electric conductors connected to the bulb-socket and the central and side electrodes respectively of the bulb and means for receiving the base of the bulb, said receiving means being by spring action held in a first position in relation to a shell of the socket when the bulb is unscrewed from the receiving means and bing movable to a second position in relation to the shell against said spring action when the bulb is screwed into the receiving means, coupling elements disposed between the conductors and said contact members on one hand breaking the contact therebetween when the receiving means is held in said first position and on the other hand closing the electric circuit to the bulb when the receiving means is brought to said second position.
To design bulb sockets in order to avoid unintentional contact with current carrying components inside the socket is previously well-known by for instance, German patent specification Nos. 472,593, 473,228, 492,234, 493,407, 906,128, 1,081,969, 1,539,415, 2,240,393, 2,262,974, 2,441,318, 2,442,063, 2,553,610, 2,651,334, 2,724,718 and 2,903,087; U.S. Pat. Nos. 2,439,385 and 3,895,195; and French patent specification No. 7,017,340 (publication number: 2,087,262), as well as Swedish patent publication Nos. 337,063, 7,202,203-1, 7,311,776-4 and 7,510,526-2.
The majority of the devices disclosed in the above-mentioned publications are based on the use of conventional receiving means for the socket (i.e., quite simply, the use of fixed thread on the inner surface of the sleeve-shaped socket shell itself) as well as a number of coupling elements which are directly or indirectly actuated by the introduction of the bulb into the receiving means and the removal of the bulb therefrom, respectively. A serious disadvantage of those devices is, however, that rather modest forces, exerted for instance by children, possible carrying electrically conductive objects, such as screw drivers, nails, screws, et cetera, are sufficient to manipulate the coupling elements and thereby render possible a switching of the coupling elements in such a manner that a current is supplied to the accessible contact members, with the ensuing risks of casualties. In order to eliminate this disadvantage, bulb sockets have been developed (see e.g. the above-mentioned U.S. Pat. No. 3,895,195) the receiving means of which are moveable in relation to the socket shell itself and are actuated by a spring force which tends to keep the receiving means in a first position in relation to the socket shell when the bulb is unscrewed, namely in a position in which the coupling elements cut the connection between the conductors and the contact members accessible in the receiving means, the receiving means being moveable against said spring force to a second position by continued rotation of the bulb after the bulb base has come into contact with the bottom of the socket shell. To try to manually move the receiving means of those bulb sockets to the position in which the coupling elements make the contact members current carrying is very difficult when the bulb is unscrewed and when a sufficiently great spring force exists. On the contrary even great spring forces are easily overcome when the bulb is screwed into the receiving means since then the thread of the bulb base exerts a powersaving wedge action in a known manner. Bulb sockets having movable spring-loaded receiving means therefore function well in comparison with other types of so called shock-proof bulb sockets.
Hitherto known bulb socket devices which are based on the use of spring-loaded movable receiving means are however--like other shock-proof bulb sockets in general--rather complicated in their structure. Thus the device disclosed for instance in U.S. Pat. No. 3,895,195 calls for a special mechanical spring, namely a compression spring, in order to achieve the necessary spring force on the receiving means, and for mounting the spring a special design of the the other components of the socket is necessary. In connection with multiple or mass production of articles of this kind it is extraordinary important that the number of components necessary and the number of working moments upon mounting thereof are as small as possible. For this reason the shock-proof bulb sockets previously known have been insignificantly used in practice, since they have been structurally complicated and accordingly badly competitive.
To combine a shortcircuiting mechanism with a device for effecting touch or shock protection in bulb sockets is per se previously known by the above-mentioned German patent specification No. 2,240,393. The bulb socket disclosed in said publication is, however, extremely complicated, and is based on the use of a receiving means fixed in the bulb socket shell rather than a movable springloaded receiving means according to the invention.